How to make brush size lock in texture paint
With Blender 2.79.

By default, with a 'tiled' brush mapping, not only the brush texture size is changed with zooming, but the brush texture is also offset when changing the angle of view.

  

However, the brush mapping can be changed to '3D' to prevent resulting in texture painting interference by view resize/change.

  

From Blender 2.79 documentation:


  The 3D option allows the brush to take full advantage of procedural
  textures. This mode uses vertex coordinates rather than the brush
  location to determine what area of the texture to use.


Note that it works perfectly with image texture as well.